Thermostat



P. R. LEE

THERMOSTAT Filed June 10, 1942 INVENTOR Fau/E Lee.

ATTORNEY WITNESSES: 5% Z 751% Patented Oct. 5, 1943 THEBMOSI'AT Paul R. Lee, Mansfield. Ohio, assignor to Westinghonse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 10, 194?, Serial No. 446,435 19 Claims. (01. 200-122) My invention relates to thermostats, and more particularly to slow make and break thermostats which are normally to operate with relatively low currents.

It is a well known feature about slow make and break thermostats that they must maintain a constant internal heat or wattage loss. It the.

internal heat loss be too high, the bimetal temperature will be higher than it should be. The thermostat will then cycle too rapidly resulting in a fluttering action of the contacts, producing radio interference and reducing the life of the contacts. If the wattage loss of the thermostat is too small, the greater portion of the tempera-' ture rise of the bimetallic element of the thermostat is produced substantially, ii' not entirely, by the heat received from the device being controlled. This feature will cause the thermostat tohave a wide temperature differential.

When using a thermostat of this character on low current circuits normally encountered with 220-volt domestic appliances, such as masters, irons, or the like, the wattage heat loss of the thermostat must be maintained at the normal value. The contact carrying arm must, therefore, have a small cross-sectional area for such low current requirements in order to increase the resistance, so as to maintain the desired necessary wattage loss.

' However, inasmuch as the contact carrying arm has a. reduced or small cross-sectional area, it follows that said arm will exert a very weak biasing force, resulting in a questionable contact pressure. This structure, therefore, causes fluttering of the contacts and, at times, even open circuits, as well as undesirably rapid cycling oi the thermostat and appliance.

In solving these problems and providing a thermostat structure which will have a constant determinable watt loss, I have provided a second movable or flexible finger which is substantially parallel to the movable contact-carrying finger. This second finger is designed primarily to maintain the necessary constant pressure while the contact-carrying finger is designed to maintain the necessary watt loss. In other words, said contact-carrying finger is to function primarily as a heater for the bimetallic element.

It is, therefore, an object of my invention to provide a creep-type thermostat having a movable contact-carrying finger and a second biasing finger parallel therewith to maintain a constant relatively heavycontact pressure.

A further' object of my invention i to provide a slow make and break creep-type thermomember.

stat which will have a constant predeterminable wattage loss.

Still a further object of my invention is to provide a thermostat havin a flexible contact finger and a second biasingfin'ger which engages the contact-carrying finger substantially in line with the movable contact carried thereby to maintain a constant biasing action in line with the movable contact at all times.

Other objects of my invention will either be pointed out specifically in the course of the following description of the device embodying my invention or will be apparent from such description and the accompanying drawing, in which:

Figure 1 is a sectional view of a device embodyin my invention;

Fig. 2 is a bottom view thereof; and

Fig. 3 is a sectional view taken along the line III-J11 of Fig. 2.

Referring to the accompanying drawing, in which like reference numerals indicate like parts in the several figures, there is shown, a thermostat ill embodying a supporting structure i2, 9. bimetallic element It, a resilient contact-carryingfin'ger l6 located below and engaged by the bimetallic member It, a second resilient finger i8 positioned beneath and substantially parallel to the contact-carrying finger i6, and supporting means i 20 for rigidly attaching the bimetallic member i4 and fingers i6 and I8 to the supporting structure l2.

The supporting structure I2 comprises, in this instance, a substantially flat rectan ular metallic An upwardly extending threaded sleeve 22 is positioned substantially at the midpointofthe base I 2 and rigidly attached thereto. In addition, a stationary contact 24 is insulatedly attached to the base i2, at one end thereofi-and the mounting mean 20 is insulatedly attached to the other end thereof. A suitable adjusting screw 26 is threadedly supported by the internally threaded bushing 22 for selectively adjusting the operation of the bimetallic element. This main combination is more clearly described and claimed in a copending application of E. K. Clark, Serial No. 394,469, filed May 21, 1941, and assigned to the assignee of this application.

Bi-metallic element i4 is a relatively fiat striptype member. Said element It is rigidly attached to the supporting means 20 by means of a resilient member 28 which, in addition, carries a second member 30. The-member 30 and bimetallic element H are rigidly attachedto the free end bias the contact-carqyin metallic strip and is ofi-set upwardly so as to be engaged by the adjusting screw 26. The resilient member 28 biases the ofi-set member 30 into contact with the adjusting screw 26 at all times. The screw 26 is thus adapted to\bodily move the bimetallic element l4 either downwardly or upwardly in response to the rotative movements of the adjusting screw 26.

The contact-carrying finger I6 is formed of a resilient current-carrying material. The width and thickness of said material is varied according to the resistance desired within said member or finger. The movable contact 25 is rigidly attached to the movable end of said finger so as to cooperate with. the stationary contact 24. An upwardly extending protuberance 34 of any suitable form on finger I6 is located relatively near the movable contact 25 and is substantially in line and normally in contact with the free end of the bimetallic member M. The bimetallic member M moves said contact-carrying finger l6 downwardly in response to an increase in temperature thereof so as to disengage the operating contacts 24 and 25.

The second resilient finger it comprises an elongated member having an upwardly extending embossed protuberance 36 located within its movable end portion. The protuberance 36 is substantially spherical in shape so as to make a point contact with finger l6. Said protuberance is positioned within the free end of the finger l8 directly in line or coaxial with the cooperating contacts 24 and 25, so as to maintain high contact pressure at all times and to ensure a positive action of said cooperating contacts during engagement and disengagemen thereof. Said second finger 18, while engaging the contactcarrying finger l6 and mounted in juxtaposition therewith, carries a relatively small amount of current due to the high electrical resistance between the two fingers. Said finger .IB .thus provides additional contact gagement with the first finger IS.

The fingers l6 and I8 are -rigidly attached to a mounting rivet or supporting member 31, for example, by being welded thereto, so as to have low electrical resistance therewith. Said rivet 31 is a part of the mounting means 20 and extends upwardly through a spacer washer '38. The upper end of said rivet or supporting member 31 is riveted or spun over upon a uitable terminal 40 in keeping with established the contact carrying finger l6 and resilient finger l8 welded to the current-carrying rivet 31, it is clear that there is a very low resistance connection therebetween.

It, therefore, follows that the resistance through the contact carrying finger it from the mounting rivet 31 or terminal 40 to the stationary contact 24 is relatively low. In contrast therewith, it will be noted that due to the protuberance 36 merely engaging the contact carrying finger l6 at a single point, the electrical resistance'from mounting rivet 31 or terminal 40 to stationary contact 24 throughthe finger l8 will be relatively high. Accordingly, the larger portion of current flowing through the thermostat ID will pass through the contact-carrying finger l6, while the finger I8 will only carry a relatively small'portion of the current. It is, therefore, obvious that the finger I8 is utilized primarily to finger l8 upwardly and to carry as small a portion of the current flowing through the thermostat as is feasible due practice. By having 1 2,es1,2o2'

to the metallurgical and structural characteristics of said finger.

It is, therefore, obvious that I have provided a thermostat having a flexible contact-carrying finger which will carry substantially all of the current passing through the thermostat and I have also provided a second resilient biasing finger l8 which engages the contact-carrying finger at substantially one point in line with the movable contact so as to maintain a positive contact pressure at all times.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof and I desire,

therefore, that only such limitations shall be placed thereon as are embodied in the prior art and the appended claims.

I claim as my invention:

1. In a thermostat having a. bimetallic ele-v ment, a movable contact-carrying member actuated by said element, a supporting structure and means for rigidly attaching said member and element to said structure, the combination of a second member mounted in juxtaposition, with said contact-carrying member, said second member biasing the contact-carrying member into a closed position, and a protuberance on said second member for engaging said contact-carrying member and constituting the sole point of contact between the movable portions of said members.

2. In a thermostat, embodying cooperating contacts, thermal responsive means, a supporting structure, and a first current-carrying arm rigidly attached to said structure, the combination of a second current-carrying arm located adjacent to said first arm and electrically in parallel therewith, the electrical resistance from one end to theother through said second arm being subpressure through enstantially greater than the resistance along said first arm, whereby the greater portion of current flowing through the thermostat will pass through said first arm.

3. In a thermostat, embodying a supporting structure, a first flexible current-carrying member attached by one end thereof to said supporting structure, a movable contact carried thereby, and a bimetallic member which flexes in response to the changes in temperature thereof mounted so as to engage and move said first current-carrying member, the combination of a second flexible current-carrying member mounted substantially parallel to said first flexible member, said first member making a high resistance engagement with said second member, whereby the resistance through said second member will be greater than that through said first member.

4. In a thermostat having a bimetallic element, a movable contact finger actuated by said element, a movable contact attached to and movable with said finger, a supporting structure and means for rigidly attaching said finger and element to said structure, the combination of a second finger mounted in juxtaposition with said contact finger, said second finger biasing the contact finger into a closed position, and a protuberance on said second finger for engaging the movable end of the contact finger, said protuberance being substantially in line with the contact carried by the contact finger.

' 5. In a thermostat, embodying a supporting structure, a first flexible current-carrying member attached by one end thereof to the supporting structure, a. movable contact carried thereby, and a bimetallic member which flexes in response to changes in temperature thereof mounted so as to engageand move said current-carrying mem- "ber, the combination of a second flexible currentcarrying member mounted substantially parallel to said first flexible member, said first member making a high resistance engagement with said second member, whereby the resistance through said second member will be greater than that through said first member, said second member having a boss-like protuberance which is substantially in line with the contact carried by the contact finger.

6. In a thermostat having a supporting structure, a bimetallic element, a first resilient contact-carrying finger actuated by said element, and means for mounting said finger on the supporting structure, the combination of a second resilient finger mounted parallel to said first resilient finger, said second finger engaging said first finger at a point in line with the movable contact carried thereby, the electrical resistance from one end of said first finger to the movable contact through the second finger being substantially higher than the direct path through the first finger, whereby the larger portion of current flowing through the thermostat will pass through the first or contact-carrying finger.

7. In a thermostat having a supporting structure, a bimetallic element, a first resilient contact-carrying finger actuated by said element, and means for mounting said finger on the supporting structure, the combination 01' a second .resilient finger mounted parallel to said first resilient finger, said second finger engaging said first finger at a point in line with the movable contact carried thereby, said second finger bias-. ing said first finger into a contact closed position and maintaining a predetermined contact pressure when said contacts are in a closed position, the electrical resistance from one end of said first finger to the movable contact through said second finger being substantially higher than the direct path through said first finger, whereby the larger portion of current fiowing through the thermostat'will pass through said first or contact carrying finger.

8. In a thermostat having a supporting structure, a'bimetallic element, a'first resilient contact-carrying member actuated by said element, and means for mounting said member on the supporting structure, the combination of a second resilient member mounted parallel to the first resilient member and rigidly attached at one end thereof in juxtaposition with said first member, the free end of said second member maintaining engagement with the free end of the first member through the biasing action of said second memberto provide a predetermined contact pressure, the electrical resistance from the stationary end of said first member to the movable contact being greater through the second member than through the first member, whereby-the current flowing through the first member will be greater than that through the second member.

9. In a thermostat having a support, a thermal responsive device, cooperating contacts including a movable contact, and a finger for carrying said movable contact, the combination of a second finger engaging the first finger in line with the movable contact for maintaining a positive contact pressure, said fingers being in parallel, with the resistance across said first finger and movable contact being relatively small and the resistance across the second finger and movable contact being relatively high.

PAUL R. LEE. 

